The question of how to feed cities may be one of the biggest contemporary questions, yet it's rarely asked. We take for granted that if we walk into a store or a restaurant, food will be there, magically coming from somewhere.

A city the size of London eats about 30 million meals every day. Where does all that food come from? Without a reliable food supply, even the most modern city would collapse quickly.

Looking at food networks offers an unusual and illuminating way to explore how cities evolved, architect Carolyn Steel says. While food is a shared necessity, it's also a shared way of thinking.

In this TEDTalk, Steel discusses the daily miracle of feeding a city and shows how ancient food routes shaped the modern world.

About Carolyn Steel

Cities, like people, are what they eat. Architect and author Carolyn Steel uses food as a medium to "read" cities and understand how they work. In her book Hungry City she traces — and puts into historical context — food's journey from land to urban table and thence to sewer.

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ALISON STEWART, HOST:

This is the TED RADIO HOUR, from NPR. I'm Alison Stewart.

On the show, we feature a number of TED talks, where our speaker shares a powerful idea with an audience gathered at a TED conference. Today, we have lots of big ideas about food.

(SOUNDBITE OF ARCHIVE RECORDING, "TED TALKS")

UNIDENTIFIED MAN #1: I think we have this whole eating thing wrong.

UNIDENTIFIED MAN #2: It's largely processed and full of all sorts of additives, extra ingredients, and you know the rest of the story.

UNIDENTIFIED WOMAN #1: We can look to the next 30 years as a time to change the food system again.

UNIDENTIFIED MAN #3: We're not born craving Whoppers or Skittles.

UNIDENTIFIED MAN #4: Sustainability is complicated, but dinner is a reality that we all very much understand.

UNIDENTIFIED MAN #5: Flavor is king. Flavor rules.

UNIDENTIFIED MAN #6: We can take the food we need from the earth, and actually heal the Earth in the process.

STEWART: It can be farm fresh or take-out; served on a white, linen tablecloth, or out of a can. But whatever's on the menu, the way we grow, transport, market and consume our food has far larger implications beyond what's on our plates.

Our guests today offer up some big ideas about food - like, how to save our crops, how to save our kids from unhealthy school lunches, and how to save ourselves from bad flavor. Let's begin with this question: Just what does it take for a city to feed itself?

CAROLYN STEEL: When you think this - every day, for a city the size of London, enough food has to be produced, transported, bought and sold, cooked, eaten, disposed of; and that something similar has to happen every day, for every city on Earth; it's remarkable that cities get fed at all.

STEWART: Carolyn Steel isn't a chef, nutritionist, or even a food writer. She's actually an architect - fascinated with the relationship between what we eat and where we live. We'll talk with Carolyn in a moment. First, let's listen to her 2009 TED talk, where she explains the ancient link between food and cities.

STEEL: About 10,000 years ago, I would say, is the beginning of this process - in the ancient Near East, known as the Fertile Crescent. And it was here, about 10,000 years ago, that two extraordinary inventions - agriculture and urbanism - happened roughly in the same place and at the same time.

And this is no accident because agriculture and cities are bound together. They need each other, because it was the discovery of grain by our ancient ancestors - for the first time produced a food source that was large enough and stable enough to support permanent settlements.

And if we look at what those settlements were like, we see they were compact. They were surrounded by productive farmland and dominated by large temple complexes that were in fact, effectively, spiritualized central food distribution centers. Because it was the temples that organized the harvest, gathered in the grain, offered it to the gods, and then offered the grain that the gods didn't eat back to the people.

So, if you like, the whole spiritual and physical life of these cities was dominated by the grain, and the harvest that sustained them. And in fact, that's true of every ancient city. But of course, not all of them were that small and famously, Rome had about a million citizens by the 1st century A.D. So how did a city like this feed itself?

Basically, Rome had access to the sea, which made it possible for it to import food from a very long way away. This was the only way it was possible to do this in the ancient world because it was very difficult to transport food over roads, which were rough; the food, obviously, went off very quickly.

So Rome effectively waged war on places like Carthage in Egypt, just to get its paws on their grain reserves. And, in fact, you could say that the expansion of the empire was really a sort of one long, drawn-out, militarized shopping spree, really.

(SOUNDBITE OF LAUGHTER)

STEEL: STEEL: In fact, I love the fact - I just have to mention this - that Rome, in fact, used to import oysters from London at one stage. I think that's extraordinary. Anyway, so Rome shaped its hinterland through its appetite.

STEWART: Carolyn Steel is joining us from London, talking about how food shapes our cities. And Carolyn, like all good architects, you brought maps to your TED talk. And one of the maps shows a 17th century London. And it's really incredible because it's a really wonderful visual because you can actually see how the pathways, and the way food came into the city, truly carved up the city.

STEEL: I just took this fabulous map; it's called the Ogilby Map. It was drawn in 1676, which is 10 years after the Great Fire of London, and it's the first accurate survey of London, so it's just beautifully detailed and - huge amount of information on it. And what I did was, I plotted onto that map how food was coming into the city. So I was literally reading historical records of the way the food was transported, and so on.

So, of course, in London, you can see the grain arriving at the grain ports and then, as the grain was arriving, it was immediately traded. So it was traded at the river ports and also the streets leading up into the middle of the city. So Bread Street tells you, you know, the - literally, you can see from the names of the streets that, you know, bread was being bought and sold on that street as well.

So the streets leading up from the grain ports to the center of the city became bread and grain markets.

STEEL: And in fact, if you look at the map of any city built before the Industrial Age, you can trace food coming into it. You can actually see how it was physically shaped by food both by reading the names of the streets, which give you a lot of clues - Friday Street on the previous slide was where you went to buy your fish on a Friday.

But also, you have to imagine it full of food, because the streets and the public spaces were the only places where food was bought and sold.

STEWART: There's a line in your talk that I want to read: This is another thing about food and cities. Once its routes into the city are established, they very rarely move. Why is that?

STEEL: This is a really interesting one. And, I mean, I guess it goes to the heart of the food problem, if you like - which is that you can't kind of sit around, you know, a table and say, look guys - you know - the food system's terrible; it doesn't work well; let's just bin it and get another one - you know? Because the food has to keep coming.

And if you think about food as a flow, it's the most important flow in the city. And if you think of it literally carving its own direction - you know, like a river in a landscape - they're established. They're very, very difficult to shift.

STEWART: They may be hard to shift, but they do transform. During your TED talk, you showed an image of the Great Western, which changed London's relationship with food. Before we get back to your talk, can you quickly explain what the Great Western is?

STEEL: It was one of the first railways built anywhere in the world, and it's a very famous railway - joined London up to the West County. But that particular image, I just love it because it's from 1840 - so it's very, very early - and it shows that, you know, the railway's actually carrying pigs and sheep - in other words, farm animals are being transported. They're no longer walking into the city.

STEEL: They're being slaughtered out of sight and mind, somewhere in the countryside, and they're coming into the city by rail. And this changes everything.

To start off with, it makes it possible for the first time to grow cities - really, any size and shape, and any place. Cities used to be constrained by geography. They used to have to get their food through very difficult physical means. All of a sudden, they're effectively emancipated from geography.

And as you can see from these maps of London, in the 90 years after the trains came, it goes from being a little blob that - it was quite easy to feed by animals coming in on foot, and so on; to a large splurge that it'd be very, very difficult to feed with anybody on foot, either animals or people.

And of course, that was just the beginning. After the trains came cars - and really, this marks the end of this process. It's the final emancipation of the city from any apparent relationship with nature at all. And this is the kind of city that's devoid of smell, devoid of mess, certainly devoid of people, because nobody would have dreamt of walking in such a landscape.

In fact, what they did to get food was they got in their cars, drove to a box somewhere on the outskirts, came back with a week's worth of shopping, and wondered what on earth to do with it. And this really is the moment when our relationship both with food and cities changes completely.

Here we have food that used to be the center of the social core of the city, at the periphery. We used to cook. Now, we just add water or, you know, a little bit of an egg, if you're making a cake or something. We don't smell food to see if it's OK to eat; we just read the back of a label on a packet. And we don't value food. We don't trust it. So instead of trusting it, we fear it. And instead of valuing it, we throw it away.

One of the great ironies of modern food systems is that they've made the very thing they promised to make easier much harder. By making it possible to build cities anywhere in any place, they've actually distanced us from our most important relationship, which is that of us and nature. And also, they've made us dependent on systems that only they can deliver; that, as we've seen, are unsustainable.

STEWART: Carolyn, how has anonymity changed our relationship to food, and to the people who produce our food? Once upon a time, you probably knew the person who planted the carrots, and you might even have known the name of the pig that you were going to eat.

STEEL: You almost certainly would have known the pig because most city dwellers kept their own pigs and their own chickens, so yes. They wouldn't have given it a name like, you know, Pinky or Perky. No, I mean, you're absolutely right. And I think there are two very, very key things that it's important to remember about our relationship with food now.

One is that what industrialization did was, it de-humanized the food chain. You know, it's even removed people from the stage where you eat the food. In other words, a lot of us now just shove food down our throats - you know - on our own, while we're on our way to something more important, rather than sitting around a table and celebrating the fact that we're eating together.

And I think, you know, our sort of transference of buying food from somebody that we trust and we know by face and by name, to relying on brands is a very, very interesting transition and obviously, one that's now taking the planet over. Because that is now what we trust - is the brands that have sold themselves to us as trustworthy in that way.

STEWART: Can you describe the final image you used in your TED talk?

STEEL: This will be the Lorenzetti "Allegory" of the effects of good government, which is an absolutely incredible fresco that was painted in 1338. And what it shows is the city and the countryside. And basically, the message is...

STEEL: If the city looks after the country, the country will look after the city. And I want us to ask now, what would Ambrogio Lorenzetti paint if he painted this image today? What would an allegory of good government look like today? 'Cause I think it's an urgent question. It's one we have to ask, and we have to start answering.

We know we are what we eat. We need to realize that the world is also what we eat. But if we take that idea, we can use food as a really powerful tool to shape the world better. Thank you very much.

(SOUNDBITE OF APPLAUSE)

STEWART: Carolyn Steel, thank you so much for joining us on the TED RADIO HOUR.

STEEL: It's been a great pleasure. Thanks so much for having me.

STEWART: Carolyn Steel is an architect, and author of "Hungry City." You can watch her TED talk, and dozens of others about food. Go to ted.com. Transcript provided by NPR, Copyright NPR.